PROJECT SUMMARY/ABSTRACT Uveal melanoma (UM) is the most common intraocular tumor in adults and accounts for approximately 5% of all melanomas. UM metastasizes primarily to the liver in 50% of patients, and currently there are no suitable treatment options. In contrast to most cutaneous melanomas, which contain mutations in BRAF or NRAS, ~90% of all uveal melanomas contain activating mutations in either GNAQ or GNA11, which code for the G?q and G?11 subunits of heterotrimeric G proteins. These two proteins are 90% homologous at the amino acid level and stimulate common signaling pathways. The activating mutations are almost always seen at the Q209 or R183 residues and render G?q/11 constitutively active when bound to GTP due to the loss of its intrinsic GTPase activity. Introduction of the GNAQ-Q209L mutant, but not wild-type GNAQ, into human or mouse melanocytes results in anchorage-independent growth and gives rise to heavily pigmented tumors in vivo. G?q/11 is involved in many downstream signaling pathways and its constitutive activity in UM leads to an increase in the activation of MAPK, Akt and the small GTPases RhoA and Rac1, which stimulates the transcription of growth promoting genes. We believe that it would be advantageous to directly inhibit oncogenic G?q/11 and prevent the activation of these various cell proliferating pathways. To this end, we have tested the compound QIC, known to specifically inhibit wild type G?q/11, and found that is also capable of inhibiting oncogenic G?q/11 found in UM. Based on these results, we hypothesize that we can use G?q/11 inhibitors such as QIC to provide a better mechanistic understanding of the role that oncogenic G?q/11 plays in UM. To test this hypothesis, we will: 1) further characterize the mechanism by which G?q/11 specific inhibitors inhibit oncogenic G?q/11 proteins in vitro; 2) assess the effects of G?q/11 inhibition on downstream signaling in uveal melanoma cells; and 3) determine the effect of G?q/11 inhibition on uveal melanoma cell growth and migration. Taken together, these studies will enable a better mechanistic understanding of the role of G?q/11 in uveal melanoma and set the stage for the use of G?q/11 inhibitors in animal models.